1. Field of the Invention
The present invention relates to an apparatus using a plasma, and more particularly, to a gas distributor for the apparatus having a supporting means.
2. Description of the Related Art
Flat panel display (FPD) devices having portability and low power consumption have been a subject of increasing research in the present information age. Among the various types of FPD devices, liquid crystal display (LCD) devices are commonly used in notebook and desktop computers because of their high resolution, capability of displaying colored images, and high quality image display.
In general, a semiconductor device or an LCD device is fabricated by repetition of a deposition step of forming a thin film on a wafer or a glass substrate, a photolithographic step of exposing some portions of the thin film using a photosensitive material, a patterning step of removing the exposed thin film and a cleaning step of eliminating a residual material. Each step of the fabrication process is performed in an apparatus under an optimum condition for each step.
FIG. 1 is a schematic cross-sectional view showing a plasma apparatus for a semiconductor device or an LCD device according to the related art. In FIG. 1, the plasma apparatus 100 includes a chamber 110 defining a reaction space, a susceptor 120 having a substrate “S” thereon and a gas distributor 140 over the susceptor 120. The gas distributor 140, which may be referred to as a shower head, includes a plurality of injection holes 142. A backing plate 150 is disposed over the gas distributor 140 and functions as a radio frequency (RF) electrode. Edge portions of the gas distributor 140 are fixed to the backing plate 150 to define a buffer space 180. The buffer space is utilized for a uniform injection of reaction gases such that the reaction gases are supplied to the buffer space 180 through a gas injection pipe 170 from an exterior gas tank (not shown) and then are primarily diffused in the buffer space.
The gas injection pipe 170 may be connected to an RF power supply 160 because the gas injection pipe 170 generally penetrates through a center of the backing plate 150. When the RF power supply 160 is connected to the gas injection pipe 170, an RF power is applied to the center of the backing plate 150 and a symmetric plasma is obtained. The susceptor 120 is movable up-and-down by a driving means (not shown) and includes a heater (not shown) therein for heating the substrate “S.” The susceptor 120 may be grounded and functions as an opposite electrode to the gas distributor 140 where the RF power is applied through the backing plate 150 from the RF power supply 160. An exhaust 130 for removing residual gases is formed through a bottom of the chamber 110 and is connected to a vacuum pump such as a turbo molecular pump.
A fabrication process in the plasma apparatus 100 is illustrated hereinafter. A robot arm (not shown) having the substrate “S” moves into the chamber 110 through a slot valve (not shown) and then the substrate “S” is loaded on the susceptor 120. Next, the robot arm moves out of the chamber 110 and the slot valve is closed. Next, the susceptor 120 moves up such that the substrate “S” is disposed in a reaction region. Next, the reaction gases injected through the gas injection pipe 170 and primarily diffused in the buffer space 180 is sprayed through the plurality of injection holes 142 of the gas distributor 140 onto the reaction region over the substrate “S.” When the RF power of the RF power supply 160 is applied to the backing plate 150, the reaction gases in the reaction region between the gas distributor 140 and the susceptor 120 are dissociated and excited to form plasma radicals having a strong oxidizing power. The plasma radicals contact the substrate “S” to form a thin film or etch a thin film. An additional RF power may be applied to the susceptor 120 to control an incident energy of the plasma radicals. Next, the susceptor 120 moves down and the robot arm moves into the chamber 110 through the slot valve. The fabrication process is completed by transferring the substrate “S” on the robot arm from the chamber 110.
The gas distributor 140 has a rectangular shape and is made of aluminum. The plurality of injection holes 142 may have a conic shape to diffuse the reaction gases. An upper portion of the conic shape has a diameter smaller than a lower portion of the conic shape. A fixing terminal 146 is formed at a periphery of the gas distributor 140. The fixing terminal 146 is fixed to a bottom surface of the backing plate 150 using a screw 192. For more stable fixation, a clamping bar 190 may be interposed between the fixing terminal 146 and the screw 192. In addition, an edge portion of the gas distributor 140 and the clamping bar 190 may be supported by a supporting means 194 extending from a sidewall of the chamber 110. The supporting means 194 includes an insulating material to prevent a leakage of the RF power.
FIG. 2 is a schematic cross-sectional view of a gas distributor 140 for a plasma apparatus according to the related art. In FIG. 2, the gas distributor 140 includes a body 144 having a rectangular plate shape and a fixing terminal 146 laterally extending from a side of the body 144. The body 144 includes a plurality of injection holes 142. The fixing terminal 146 includes a first horizontal portion 146a, a vertical portion 146b and a second horizontal portion 146c. The fixing terminal 146 has a thin plate shape extending from sidewall of the body 144 and bent twice in a three-dimensional view.
The gas distributor 140 of FIG. 2 may sag at a central portion due to a mass thereof and a thermal transformation. FIG. 3 is a schematic cross-sectional view showing a bending momentum of a gas distributor for a plasma apparatus according to the related art. In FIG. 3, a gas distributor 140 has a downward bending momentum at a central portion of a body 144 because of a thermal transformation. The thermal transformation is caused by a thermal expansion due to a high temperature plasma and/or a heat radiated from a heater in a susceptor 120 (of FIG. 1). Even though the body 140 may expand vertically, the thermal transformation of the body 140 is mainly generated by the horizontal thermal expansion. Since a high temperature plasma and a heater are disposed under the gas distributor 140, a lower portion of the body 144 horizontally expands greater than an upper portion with respect to a mass center surface of the body 144. Accordingly, a downward bending momentum (toward the susceptor 120) is generated at a central portion of the body 144. In addition, the body may be downwardly warped by the gravitation. Therefore, the gas distributor 140 may sag at a central portion due to the downward bending momentum. As a result, a distance between the gas distributor 140 and the susceptor 120 at a central portion of the body 144 is greater than that at a periphery of the body 144. Reaction gases in a reaction space have a non-uniform concentration, thereby deteriorating a process uniformity.
FIG. 4 is a schematic cross-sectional view of another gas distributor according to the related art. In FIG. 4, a gas distributor 140 has a flexible fixing terminal 146 to release a bending momentum. When the body 140 horizontally expands, the vertical portion 146b of the fixing terminal 146 is outwardly pushed and partially receives the horizontal thermal expansion. Accordingly, the downward bending momentum due to the mass of the body 144 and the thermal expansion is relieved. However, the flexible fixing terminal 146 only partially relieves the downward bending momentum and can not remove a sag of the body 144. Since the fixing terminal 146 extends from an upper portion of the body 144 with respect to a mass center surface, an expansion in a lower portion of the body 144 is not restrained and the gas distributor 140 has a sag.